CN107005516B

CN107005516B - Inter-block interference suppression using null guard intervals

Info

Publication number: CN107005516B
Application number: CN201480084338.8A
Authority: CN
Inventors: A.加塔米
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2014-12-23
Filing date: 2014-12-23
Publication date: 2021-03-19
Anticipated expiration: 2034-12-23
Also published as: CN107005516A; US10257004B2; EP3238398B1; EP3238398A1; WO2016102007A1; US20170359207A1

Abstract

A method of transmitting data over a wireless communication channel, the method comprising transmitting a plurality of blocks (70), wherein each block (70) comprises a plurality of symbols (71, 72, 73, 74, 75) representing the data. The symbols are transmitted using time packing or fast-than-Nyquist signaling such that each symbol in a block overlaps with at least one other symbol in the block in the time domain. A null guard interval (77) having a length (meaning that intersymbol interference is not a cause of intersymbol interference) is included in each block.

Description

Inter-block interference suppression using null guard intervals

Technical Field

The present invention relates to wireless communications, and in particular to wireless communications using fast-than-Nyquist signaling.

Background

When a signal consisting of a plurality of symbols arranged in blocks is transmitted over a wireless communication channel, there is a high probability that the signal will be received with some form of distortion. For example, the signal may arrive at the receiver along multiple paths (such as a direct line-of-sight path and one or more reflected paths). Such distortion has the potential to cause intersymbol interference or intersymbol interference.

To avoid intersymbol interference, the Nyquist criterion sets the conditions that the channel and the transmitted symbols must satisfy. One aspect of the Nyquist criterion is that for a given channel, the criterion sets a lower limit on the time separation of the data-carrying pulses.

It is also known that it is possible to transmit signals in the form of Nyquist pulses but with a shorter inter-pulse time separation than that specified by the Nyquist criterion. This is called fast-than-Nyquist signalling. This has the advantage that it can increase data throughput. However, it has the adverse effect that there will be intersymbol interference, i.e. the samples obtained at the receiver will depend on more than one transmitted symbol. There is an increased chance of error in the receiver.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a method of transmitting data over a wireless communication channel, the method comprising transmitting a plurality of blocks, each block comprising a plurality of symbols representing the data, and transmitting the symbols using time packing (time packing) such that each symbol in a block overlaps in the time domain with at least one other symbol in the block. The method also includes including a null guard interval in each block.

According to a second aspect of the present invention there is provided a transmitter for transmitting data over a wireless communication channel, the transmitter being configured to transmit a plurality of blocks, each block comprising a plurality of symbols representing the data, and to transmit the symbols using time packing such that each symbol in a block overlaps with at least one other symbol in the block in the time domain. A null guard interval is included in each block.

According to a third aspect of the present invention there is provided a method of receiving data over a wireless communication channel, comprising receiving a plurality of blocks, each block comprising a plurality of symbols representing said data, wherein said symbols have been transmitted using time packing such that each symbol in a block overlaps in the time domain with at least one other symbol in said block. Each block includes an empty guard interval.

According to a fourth aspect of the present invention, there is provided a receiver for receiving data over a wireless communication channel, the receiver being configured to receive a plurality of blocks, each block comprising a plurality of symbols representing the data, wherein the symbols have been transmitted using time packing such that each symbol in a block overlaps with at least one other symbol in the block in the time domain. Each block includes an empty guard interval.

According to a fifth aspect of the invention there is provided a computer program product comprising a computer readable storage medium containing instructions for causing an apparatus to perform the method according to the first or third aspect.

Drawings

Fig. 1 is a schematic illustration of a communication system in accordance with an embodiment.

Fig. 2 is a more detailed illustration of the communication system of fig. 1.

Fig. 3 shows a diagram illustrating the form of signals transmitted in the communication system of fig. 1 and 2.

Fig. 4 illustrates a method according to an embodiment.

Detailed Description

Fig. 1 shows a communication system comprising a transmitter 10 and a receiver 20.

The transmitter 10 comprises a communication module 12 and a data processing and control unit 14. The data processing and control unit 14 includes a processor 16 and a memory 18. The processor 16 performs data processing and logical operations, and the memory 18 stores program instructions and working data for causing the processor to perform the methods described herein. The communication module 12 generates signals in a suitable form for transmission in accordance with a suitable communication standard.

Similarly, the receiver 20 comprises a communication module 22 and a data processing and control unit 24. The data processing and control unit 24 includes a processor 26 and a memory 28. The processor 26 performs data processing and logical operations, and the memory 28 stores program instructions and working data for causing the processor to perform the methods described herein. The program instructions may be provided in the form of a computer program product containing the instructions in a computer readable form. The communication module 22 receives signals that have been transmitted in accordance with the appropriate communication standard and extracts data from the received signals.

Although fig. 1 shows a transmitter 10 and a receiver 20, it will be appreciated that in many applications the communication between two devices is bidirectional. That is, when a first device transmits a signal to a second device, the second device may also transmit a signal to the first device at the same time as the first device is transmitting, or at a different time. Thus, the transmitter 10 and receiver 20 may be included in any fixed or portable device for wireless communication, including but not limited to laptop or tablet computers, cellular telephones including smart phones, cellular base stations or wireless access points, or remote sensors for machine-to-machine communication.

As shown in fig. 1, the transmitter 10 and the receiver 20 communicate through a wireless communication channel 30.

Fig. 2 shows in more detail the form of signals generated, transmitted, received and extracted in the transmitter 10 and the receiver 20.

In particular, FIG. 2 shows a system using fast-than-Nyquist signaling (where time packing is used). I.e. Nyquist pulses are generated at a sampling rate based on the sample period T. However, instead of pulsing at times separated by T seconds, the pulses are instead pulsed at ρTSeconds are sent separately, where 0< ρ <1. As such, the symbols are transmitted in a non-orthogonal form.

As discussed in more detail below, the received input data is applieda[n]To precoder 40 to obtain precoded data. Applying precoded dataâ[n]To the pulse filter 42 to generate a signal for transmission. In one embodiment, the data is modulated using Pulse Amplitude Modulation (PAM)â[n]As an amplitude for the pulse. However, it will be appreciated that other modulation schemes may be used.

In order to generate a signal in a form suitable for transmission using fast-than-Nyquist signalling, a pulse filter 42 acts on the precoded dataâ[n]To obtain a transmitted signals(t)Wherein:

wherein

Is a new pulse shape that is standardized so as not to increase the transmit power in the receiver. Other pulse filters are possible.

When transmitting signals over the wireless channel 30s(t)(which can be seen as causing Additional White Gaussian Noise (AWGN)), this gives the received signalr(t)Comprises the following steps:

whereinw(t)Is a stable, white, gaussian process.

As shown in fig. 2, the received signal is filtered using a matched filter 50r(t)Sampling to optimize signal-to-noise ratio (SNR) and obtaining for signal estimationSufficient data points of the metery[n]A collection of (a). Thus:

the challenge then in the receiver is to give the sampley[n]To estimate the raw input data with the lowest possible error probabilitya[n]。

It is determined that the sampley[n]According to the following formula and transmitted dataâ[n]And noisew(t)And (3) correlation:

where w is the gaussian noise expressed as a variable that is independent and identically distributed (i.i.d.), and G is a matrix whose elements are given as follows:

the form of the matrix G thus depends on the form of the particular pulse shaping filter used. The precoding applied by precoder block 40 mentioned above is sample-basedy[n]Data to be transmittedâ[n]、And noisew(t)The relationship between them. The precoding is based on the pulse shape from the pulse shaping filter. The precoding is also based on the amount of overlap of the symbols in the fast-than-Nyquist form (e.g., as indicated by the parameter ρ).

Specifically, the precoding used in the precoder block 40 is referred to as G-to-minus-half (GTMH) precoding. This is described in "Low complexity algorithms for fast-than-Nyquist signaling", Emil Ringh, MSC discourse Collection, St.Cologol, Sweden, 2013. Instead of using input data bits

These are converted into precoded bits as amplitudes of the PAM symbolsâWhich isIn

And symbolâAlso taken from an alphabet a which may for example consist of binary digits in real or complex form.

Thus applying precoding bits prior to transmissionâTo the pulse filter 42. After transmission over the wireless channel, the received signal is passed to a matched filter 50. In this example, the precoding is G to halve (GTMH), and optionally, G is a matrix whose form depends on the form of the pulse shaping filter.

Data samples obtained by matched filter 50y[n]And then supplied to a G-to-halve (GTMH) decoding block 52. Thus, the data samples are convertedy[n]To decode the samplesŷ[n]。

The purpose of the receiver is to provide a given data sampley[n]To the input data bitaIs estimated.

Using input data bitsaAnd precoded bitsâThe relationship between, the previously derived relationship

Can be rewritten as:

thus, by applying G-to-halve (GTMH) decoding in block 52, the received data samples are converted using the following equationy[n]To obtain decoded samples:

or

It can be seen that

This has the effect of sampling data fromy[n]Obtaining decoded samplesŷ[n]The receiver can obtain a value that can then be used to obtain an estimate of the input data.

Specifically, as one example, to arrive at an input data bitaUsing any conventional channel estimation algorithm, and then the decoded samples can be decodedŷ[n]Applied to a Maximum Likelihood (ML) estimation block (not shown in fig. 2).

The effect of GTMH-precoding is thus to reduce the complexity of the estimation that has to be performed in the receiver in this particular case of fast-than-Nyquist signalling.

One problem that still arises with respect to fast-than-Nyquist signaling is inter-symbol interference. Fig. 3 illustrates a method for transmitting symbols using fast-than-Nyquist signaling in a manner that mitigates or avoids the possibility of inter-block interference.

In particular, fig. 3 shows a block 70 containing

symbols

71, 72, 73, 74, 75 representing precoded input data. Although fig. 3 shows the entirety of only one block 70, it also shows the end of the preceding block 70a and the beginning of the subsequent block 70 b. The transmission from the conveyor contains a series of such blocks, which may all have the general form shown in fig. 3.

In the general case, a block contains a first number N of symbols. Thus, in this illustrated example, N = 5. In a typical case, the number of symbols in a block is predetermined and known in advance by the transmitter and the receiver.

Each symbol having a durationTWhich is referred to herein as a standard symbol period, which may be, for example, a Nyquist symbol period. Thus, when using an orthogonal transmission scheme, the beginning of the symbols are separated in time by a standard symbol period or pulse duration T, and N symbols occupy period N.T.

However, because of the use of fast-than-Nyquist signalling, the start of successive pulses not being in accordance with the pulse duration T, but rather in accordance with a shorter period ρT(i.e., 0)< ρ <1) Are separated in time, and thus the effect is that during a period such as period 76, two successive pulses (i.e.

pulses

71, 72 in this case) overlap.

In this illustrated example, the effect of using shorter pulse separations is that the first number of symbols, N, occupies a second integer number of standard symbol periods, the second number being smaller than the first number. In this example, the second number is one less than the first number, and thus the N symbols occupy (N-1) standard symbol periods. To achieve this, one can see a reduced pulse separation ρ = (d =: (d))N - 2)/(N-1). Alternatively, ρ = (N-1)/N.

In other examples, the effect of using shorter pulse separations is that the first number of symbols, N, occupies a second number of standard symbol periods, where the second number is less than the first number by more or less than one standard symbol period. The second number need not be an integer.

Further, as shown in fig. 3, block 70 includes a guard interval 77 during which no symbol or any portion of any symbol is transmitted. No repeated cyclic prefix is transmitted within the guard interval 77. I.e. the guard interval 77 is an empty guard interval.

In this illustrated example, a guard interval 77 follows the

symbols

71, 72, 73, 74, 75. The next block (e.g., block 70b shown in fig. 3) immediately follows the end of the guard interval 77. In an alternative embodiment, a guard interval can be included at the beginning of each block with similar effect.

Thus, a plurality of blocks are transmitted, each block comprising a plurality of symbols representing data, the symbols being transmitted using time packing such that each symbol in the block overlaps with at least one other symbol in the block in the time domain, and each block further comprises a null guard interval.

In a preferred embodiment, the data processing and control unit 14 of the transmitter 10 is capable of interpreting the signals received by the communication module 12 in order to measure or estimate the inter-symbol interference caused by the channel. The amount of inter-symbol interference can be assessed in terms of the number of consecutive symbols interfering with each other. For example, in the case of intersymbol interference caused by multipath effects, this is a function of the difference in path length between the line-of-sight transmission path and the longest detectable echo path. This difference can then be expressed in terms of symbol periods. If the difference is less than one symbol period, two consecutive symbols will interfere with each other. If the difference is greater than one symbol period but less than two symbol periods, then one symbol will interfere not only with the next symbol, but also with the symbol following that next symbol. For still larger differences, a symbol will interfere with more other symbols.

E.g., by the data processing and control unit 14 of the transmitter 10, the length of the guard interval can then be selected and the transmitter 10 can transmit signals such that inter-block interference is mitigated or avoided despite the presence of inter-symbol interference due to the effect of the channel and due to the use of fast-than-nyquist (ftn) signaling. Thus, in a system where the channel is such that there is intersymbol interference between two consecutive symbols, the null guard interval can be chosen such that it has a duration of one symbol period T (as shown in fig. 3). This has the effect that there is no intersymbol interference between the last symbol of one block and the first symbol of the next block and therefore no intersymbol interference. This therefore allows the use of FTN signalling as described above and/or the use of GTMH precoding as described above.

Where the effect of channel dispersion or multipath means that intersymbol interference can exist between more than two consecutive symbols (i.e. the channel is longer than 2 taps), the inclusion of a longer null guard interval is necessary to ensure that there is no intersymbol interference. The length of the null guard interval can thus be chosen such that it is longer than the length at which intersymbol interference occurs. The length of the null guard interval can be chosen to be an integer number of symbol periods or a non-integer number of symbol periods. In some examples, the guard interval is based on the determined number of channel taps. For example, the guard interval is equal to or longer than the duration of a number of symbols, where the number corresponds to the number of channel taps minus one.

Where inter-symbol interference caused by the channel is measured, the length of the null guard interval can be adapted in-flight (on the fly) to account for varying channel conditions as the system is in use. In some examples, any changes may be signaled between the transmitter and the receiver. In some examples, a method includes measuring a degree of inter-symbol interference of the channel; and setting a length of the null guard interval in response thereto.

Thus, fig. 2 shows a null guard interval of suitable length inserted into the signal before transmission, and conversely shows the guard interval removed in the receiver before passing the signal to the matched filter 50. In the embodiment shown in FIG. 3, fast-than-Nyquist signaling is used atN-1) transmitting a block of N symbols during a symbol period. Also, the null guard interval has a duration of one standard symbol period. The overall effect is that the block therefore contains N symbols and has a duration of N standard symbol periods. In another embodiment, where it is found useful to use a null guard interval having a longer duration (e.g., a duration of M symbol periods), fast-than-Nyquist signaling may be used to transmit a block of N symbols during (N-M) symbol periods. The overall effect is once again that the block contains N symbols and has a duration of N symbol periods.

However, in other examples, a block of N symbols may be transmitted during (N-P) symbol periods using fast-than-Nyquist signaling, where the null guard interval has a duration less than P symbol periods, and thus the overall effect is that the block contains N symbols in a duration shorter than N symbol periods. In yet a further example, a block of N symbols may be transmitted during (N-P) symbol periods using fast-than-Nyquist signaling, where it is decided to use a null guard interval having a duration greater than P symbol periods, and thus the overall effect is that the block contains N symbols for a duration longer than N symbol periods.

Fig. 4 illustrates a method 100 in accordance with one or more examples. Embodiments may be only part of the steps shown.

In the transmitter, data is received in 101. At 102, the data is pre-coded for fast-than-Nyquist ingress. Optionally, the precoding is based on the filter 42. For example, the method includes applying precoding to the input data; and passing the precoded input data to a pulse shaping filter. In 103, the signal is filtered, for example by a pulse filter 42. At 104, a guard interval is inserted prior to transmission over the channel. In 105, the signal is transmitted.

In 106, the receiver receives the transmitted signal from the wireless channel. In 107, the guard interval is removed. At 108, the signal is filtered using the matched filter 50. In 109, the fast-than-Nyquist signal is decoded. At 110, the transmitted data is evaluated.

Thus, a method and system are described in which signals for transmission can be transmitted using time packing, wherein guard intervals are inserted in order to ensure that inter-block interference is mitigated.

In one embodiment, there is provided a method of transmitting data over a wireless communication channel, the method comprising: transmitting a plurality of blocks, each block comprising a plurality of symbols representing the data. The method further comprises transmitting the symbols using time packing such that each symbol in a block overlaps with at least one other symbol in the block in the time domain; and including empty guard intervals in each block.

Any examples of the apparatus and method may be combined with any other examples of the apparatus and method.

Claims

1. A method of transmitting data over a wireless communication channel, the method comprising:

transmitting a plurality of blocks (70), each block (70) comprising a plurality of symbols (71, 72, 73, 74, 75) representing the data,

wherein transmitting the plurality of blocks (70) comprises:

transmitting the plurality of symbols (71, 72, 73, 74, 75) using time packing such that each symbol in a block (70) overlaps with at least one other symbol in the block (70) in the time domain; and

including a null guard interval (77) in each block (70), wherein no symbol or any portion of the symbol is transmitted during the null guard interval (77), and

wherein the time packing is such that each block (70) comprises a first number of symbols and the duration of the block (70) comprising the null guard interval (77) is shorter than the duration of the first number of standard symbol periods.

2. The method as claimed in claim 1, wherein transmitting the plurality of symbols (71, 72, 73, 74, 75) using the time packing comprises transmitting the plurality of symbols (71, 72, 73, 74, 75) using fast-than-Nyquist signaling.

3. The method as claimed in claim 2, further comprising:

applying precoding (40) to the input data; and

the precoded input data is passed to a pulse shaping filter (42).

4. A method as claimed in claim 3, wherein said precoding (40) is G to minus half GTMH, and wherein G is a matrix whose form depends on the form of said pulse-shaping filter (42).

5. A method as claimed in any one of claims 1 to 4, wherein said time packing is such that each block (70) comprises said first number of symbols, said first number of symbols being transmitted during a time period equal to a second number of standard symbol periods, said second number being less than said first number.

6. A method as claimed in claim 5, wherein said second number is one less than said first number.

7. A method as claimed in any one of claims 1 to 4, wherein said null guard interval (77) has a duration equal to an integer number of standard symbol periods (T).

8. A method as claimed in claim 7, wherein said null guard interval (77) has a duration equal to one symbol period.

9. A method as claimed in any one of claims 1 to 4, wherein the empty guard interval (77) is included at the end of each block (70).

10. The method as claimed in any one of claims 1 to 4, further comprising:

measuring an inter-symbol interference level of the wireless communication channel; and

in response thereto, the length of the empty guard interval (77) is set.

11. A method as claimed in claim 10, wherein the length of the null guard interval (77) is set in such a way as to avoid inter-block interference.

12. A transmitter for transmitting data over a wireless communication channel, the transmitter comprising a communication module and a data processing and control unit, and the transmitter being configured to:

wherein to transmit a plurality of blocks (70), the transmitter is further configured to transmit the plurality of symbols (71, 72, 73, 74, 75) using time packing such that each symbol in a block (70) overlaps with at least one other symbol in the block (70) in the time domain; and

13. A transmitter as claimed in claim 12, further comprising:

means for applying a precoding (40) to the input data; and

a pulse shaping filter (42) connected to receive the precoded input data and to generate the plurality of symbols (71, 72, 73, 74, 75) for transmission.

14. A transmitter as claimed in claim 13, wherein the precoding (40) is G to minus half GTMH, and wherein G is a matrix whose form depends on the form of the pulse-shaping filter (42).

15. A transmitter as claimed in any one of claims 12 to 14, wherein the time packing is such that each block (70) comprises the first number of symbols, which are transmitted during a time period equal to a second number of standard symbol periods, which second number is smaller than the first number.

16. The transmitter as claimed in any of claims 12 to 14, further configured to:

in response thereto, the length of the empty guard interval (77) is set.

17. A transmitter as claimed in claim 16, wherein the length of the null guard interval (77) is set in a manner to avoid inter-block interference.

18. A method of receiving data over a wireless communication channel, the method comprising:

receiving a plurality of blocks (70), each block (70) comprising a plurality of symbols (71, 72, 73, 74, 75) representing the data,

wherein the plurality of symbols (71, 72, 73, 74, 75) have been transmitted using time packing such that each symbol in a block (70) overlaps with at least one other symbol in the block (70) in the time domain,

wherein each block (70) comprises a null guard interval (77),

wherein no symbol or any part of the symbol is transmitted during said spatial guard interval (77), and

19. The method as claimed in claim 18, further comprising:

passing the received signal to a filter matched to a pulse shaping filter (42) in the transmitter; and

the output of the filter is passed to a decoder corresponding to a precoding block (40) in the transmitter.

20. A method as claimed in claim 19, wherein said decoder performs G to minus half GTMH, and wherein G is a matrix whose form depends on the form of said pulse-shaping filter (42).

21. A method as claimed in any one of claims 18 to 20, including extracting the empty guard intervals (77) from the end of each block (70).

22. A receiver for receiving data over a wireless communication channel, the receiver comprising a communication module and a data processing and control unit, and the receiver being configured to:

wherein each block (70) comprises a null guard interval (77),

23. A receiver as claimed in claim 22, comprising:

a filter (50) matched to a pulse shaping filter (42) in the transmitter for filtering the received signal; and

a decoder (52), corresponding to the pre-coding block (40) in the transmitter, for decoding the filtered received signal.

24. The receiver as claimed in claim 23, wherein said decoder (52) performs G-to-minus-half GTMH decoding, and wherein G is a matrix whose form depends on the form of said pulse-shaping filter (42) in said transmitter.

25. A computer readable storage medium containing instructions for causing an apparatus to perform the method as claimed in any one of claims 1 to 11 or 18 to 21.